In contemporary off shore installations, for example oil and gas production platforms, drilling rigs, offshore wind energy facilities, ocean wave energy facilities and mining activities, there often arises a need to transfer considerable electrical power, for example for providing electrical power to electric motors and for coupling outputs from electrical generators. Such transfer of considerable power is beneficially achieved at elevated potentials in an order of kilovolts (kV) for reducing an amount of associated electrical current flowing in electrical wires and cables. It is contemporarily found in practice difficult to provide high-reliability electrical connections in underwater environments, especially when elevated operating potentials are required. Saline seawater leaks, or even elevated humidity resulting from ingress of seawater at elevated operating pressures, are susceptible to cause flashovers and associated short circuits in electrical apparatus. Electrical flashover damage is often permanent when polymer insulators become thereby charred and/or ablated.
Power transfer via magnetic coupling through connector elements which are susceptible to being coupled together and mutually uncoupled is known from a published United Kingdom patent no. GB 2 318 397A (Wilson, GEC). There is described a connector comprising a pair of pistons defining respective mating surfaces. One of the pistons is mounted within a bore in a first support member for movement along a first axis and arranged to engage a resilient seal mounted within the bore. Another of the pistons is mounted within a bore in a second support member for movement along a second axis that is parallel to the fist axis and arranged to engage a resilient seal mounted within the bore. The first and second support members are arranged for relative movement only in a direction at right angles to first and second axes for enabling the two axes to be mutually aligned. Springs are included for biasing the pistons towards each other such that their mating surfaces operably wipe each other during alignment of the two axes. The magnetic coupling also includes a fluid connector for admitting pressurized fluid between each piston and its associated support member whereby, in operation, the aligned pistons are operable to press the mating surfaces together.
Such a known magnetic coupling has several potential operating problems associated therewith. For example, fluid connection to the pistons creates for complication with yet more fluid-bearing tubes that are susceptible to rupture under high operating pressures. Moreover, the wiping action of the abutting surfaces is potentially inadequate for avoiding significant build up of non-magnetic growth onto the abutting mating surfaces. Furthermore, known magnetic couplings are also potentially difficult to manoeuvre and align during attachment in underwater environments where optical viewing is impaired, for example as a consequence of silt or marine microbes.
These contemporary known systems suffer many problems which render them unsuitable for coupling significant power in an order to tens, or even hundreds, of kilowatts (kW) magnitude.